The invention relates to a windshield for motor vehicles with a reflecting arrangement which allows optical information or signals to be reflected in the windshield and made visible in the driver's field of view, as a result of which the optical information is recognizable by the driver within the same field of view as is suitable for the observation of the traffic.
In the case of windshields of this type, important information and warning signals may be observed by the driver without there being any need for the driver to change his direction of vision from the traffic in front of him. The optical elements conveying the optical information and/or signals are disposed, as a rule, within the dashboard. In the case of a known windshield of this type, the reflecting arrangement is a partially reflective, thin metal layer which must allow sufficient transmission of light in order to ensure the required transparency of the windshield, even in the area of this layer.
The optical information or signals are not only reflected by the partially reflective layer as such, but also at the glass-air or glass-synthetic material layer interfaces These undesirable reflections lead to double images which disturb the observation of useful information, since the reflected primary light is relatively weak and even light striking the dashboard from the most diverse directions will be reflected and form a disturbing background against which the relatively weak useful signals show little contrast.
In order to eliminate these disturbing double images, it has been known to select the geometric arrangement in such a way that the angle of incidence of the light rays coming from the signal transmitters lies in the order of magnitude of the Brewster angle, and to dispose a polarization filter in the path of rays of the image to be observed which extinguishes the polarized light rays reflected at the surfaces of the glass (German Pat. No. 24 50 704). In the case of this known arrangement, the disturbing double images are eliminated. However, this known arrangement is still not without disadvantages. These include the fact that the predetermined angle of incidence calls for a certain geometric arrangement of the windshield and/or of the irradiation arrangement. These disadvantages also include the fact that the partially reflecting layer, especially in the case of direct illumination by the sun from the outside, acts as a strongly reflecting mirrored surface and may bring about the undesirable blinding of other motorists. Furthermore, the reflected image of the signals recognizable from inside of the vehicle depends, perforce, on the planimetrics of the reflecting surface. Since windshields as a rule are not flat but curved, it is unavoidable that the reflected image will be rendered correspondingly distorted. Any difficulty in viewing the image is then further compounded by the high transparency required of the partially reflecting layer, which allows only a relatively small portion of the light incident on this layer to be reflected. Therefore, depending upon the brightness of the surroundings, the signal reflected in the windshield may appear relatively weak.